JP2011514009A - Optical synchronization based on optical resonator with high quality factor - Google Patents

Abstract

TECHNIQUE AND DEVICE FOR PROVIDING OPTICAL RESONATOR AND LASER OPTICAL SYNCHRONIZATION

Description

Priority claim and related patent applications This application is filed on March 11, 2008, US Provisional Application No. 61 / 035,608, entitled "Tunable Narrow-Linewidth Injection-Locked Semiconductor Lasers". with High-Q Whispering-Gallery Mode Resonators ", US Provisional Application No. 61 / 053,411, filed May 15, 2008, title of invention," VERY PRECISE OPTICAL LOCK FOR BALANCED WGMR BASED FILTER ", Claims the priority of US Provisional Application No. 61 / 058,487, the title of the invention, "ALL OPTICAL LOCK FOR PHOTONIC APPLICATIONS", filed July 3, 2008. The entire disclosure of these patent applications is incorporated by reference as part of this application.

  The present invention relates to devices based on optical resonators.

  The optical resonator can be configured to exhibit a high resonator quality factor (Q value) for various applications such as, for example, optical frequency reference and optical filtering devices. For example, a whispering gallery mode (WGM) resonator has a structure for confining light in a whispering gallery mode, and the light is totally reflected in a closed ring optical path. The light in the WGM resonator cannot exit the resonator by light transmission, and as a result, by using the WGM resonator, a high light quality factor (Q that is difficult to achieve with a Fabry-Perot resonator) Value) can be realized. Light in the WGM resonator “leaks” from the outer surface of the closed annular optical path of the WGM resonator via the WG mode evanescent field.

  This specification discloses examples of techniques and devices for providing optical synchronization of optical resonators and lasers.

  In one aspect, the present application provides a device that includes a laser that generates a laser, an optical interferometer, and an optical resonator connected to the optical interferometer. The laser produces a laser output beam at the laser frequency. The optical interferometer is located in the optical path of the laser output beam, the first optical path receiving the first portion of the laser output beam, the second optical path receiving the second portion of the laser output beam, and the first and first An optical coupler including two optical paths that end together is included. The optical coupler transmits a portion of the light from the first optical path and reflects a portion of the light from the second optical path to generate a first combined light output. The optical coupler also transmits a portion of the light from the second optical path and reflects a portion of the light from the first optical path to generate a second combined light output. The optical resonator is optically coupled to the first optical path and filters light in the first optical path. The device detects a first combined light output and a second combined light output to generate an error signal representing a frequency difference between the laser frequency and the resonant frequency of the optical resonator A feedback control mechanism that receives the error signal and tunes one of the laser and (2) the optical resonator in accordance with the frequency difference of the error signal to synchronize the laser and the optical resonator with each other. Prepare.

  In another aspect, a method of synchronizing a laser and an optical resonator includes operating a laser and generating a laser output beam at a laser frequency without modulating the laser beam; and Directing to an optical interferometer that includes a first optical path and a second optical path that intersect, and generates optical interference between the light in the first optical path and the light in the second optical path, and the first optical path Optically coupling an optical resonator therein to filter the light in the first optical path, and using the two optical outputs of the optical interferometer, the laser frequency of the laser and the resonant frequency of the optical resonator Generating an error signal representing a frequency difference between and (1) tuning one of the laser and (2) the optical resonator according to the frequency difference of the error signal, Steps to synchronize with each other With the door.

  In another aspect, a device is provided that stabilizes the resonant frequency of the optical resonator relative to the laser frequency from the laser. The device includes a laser that generates a laser output beam at a laser carrier frequency, an optical resonator that is disposed in the optical path of the laser output beam, receives the light of the laser output beam, and couples the optical resonator to the optical path to output the laser An optical coupler that receives the light of the beam and generates an optical output. The optical coupler provides optical coupling at an optical filter mode frequency different from the laser carrier frequency so as to provide optical coupling that is not under critical coupling conditions in which the light coupled to the optical resonator is completely trapped within the optical resonator. Constructed and arranged with respect to the resonator. The device includes an optical modulator disposed in the optical path of the laser output beam between the laser and the optical resonator, and modulates the laser output beam to generate a modulation sideband. Optical coupling of light in the waveband to the optical resonator is near the critical coupling condition, and the optical resonator is thermally stabilized by light absorption of light in the modulation sideband. The modulation sideband is different in frequency from the optical filter mode frequency.

  In another aspect, a method of operating an optical resonator filter includes providing a resonator controlled laser beam of a laser carrier frequency modulated to carry a modulation sideband to an optical resonator, and an optical coupler. Operate and couple the light in the modulation sideband to the optical resonator near the critical coupling condition where the light coupled to the optical resonator is completely trapped in the optical resonator, Stabilizing the optical resonator thermally by absorbing light, and optically resonating by directing the incident optical signal while the optical resonator receives and stabilizes the optical resonator-controlled laser beam And optical filtering of the incident optical signal by resonance of the optical resonator at an optical filter mode frequency different from the laser carrier frequency of the modulation sideband and the resonator-controlled laser beam. .

  In yet another aspect, a device for synchronizing a laser to an optical resonator is tunable in response to a control signal, a distributed feedback (DFB) laser that generates a laser beam at a laser frequency, and an optical Configured to support a whispering gallery mode circulating in the resonator, optically coupled to the DFB laser, receiving a portion of the laser beam in the whispering gallery mode optical resonator, An optical resonator is provided that returns whispering gallery mode laser light to the DFB laser, stabilizes the laser frequency at the whispering gallery mode frequency, and reduces the line width of the DFB laser. The device further comprises a resonator tuning mechanism that controls and tunes the frequency of the whispering gallery mode to tune the laser frequency of the DFB laser via feedback of the laser light from the optical resonator to the DFB laser.

  These and other aspects and embodiments are disclosed in detail in the drawings, description, and claims.

It is a figure explaining the specific example and operation | movement which synchronize a laser and a resonator via an optical interferometer. It is a figure explaining the specific example and operation | movement which synchronize a laser and a resonator via an optical interferometer. It is a figure explaining the specific example and operation | movement which synchronize a laser and a resonator via an optical interferometer. It is a figure explaining the specific example and operation | movement which synchronize a laser and a resonator via an optical interferometer. It is a figure explaining the specific example and operation | movement which synchronize a laser and a resonator via an optical interferometer. It is a figure explaining the specific example and operation | movement which synchronize a laser and a resonator via an optical interferometer. It is a figure explaining the specific example and operation | movement which synchronize a laser and a resonator via an optical interferometer. It is a figure explaining the specific example and operation | movement which synchronize a laser and a resonator via an optical interferometer. It is a figure explaining the specific example and operation | movement which synchronize a laser and a resonator via an optical interferometer. It is a figure explaining the specific example and operation | movement which synchronize a laser and a resonator via an optical interferometer. It is a figure explaining the specific example and operation | movement which synchronize a laser and a resonator via an optical interferometer. It is a figure explaining the specific example and operation | movement which synchronize a resonator with a laser by thermal stabilization using the light in a modulation sideband. It is a figure explaining the specific example and operation | movement which synchronize a resonator with a laser by thermal stabilization using the light in a modulation sideband. It is a figure explaining the specific example and operation | movement which synchronize a resonator with a laser by thermal stabilization using the light in a modulation sideband. FIG. 6 shows a device that achieves a narrow laser linewidth by synchronizing the laser to the resonator by injection locking.

  The optical synchronization techniques and devices disclosed herein provide a narrow resonator linewidth using an optical resonator having a high Q value. An optical resonator with a high Q value can be synchronized to the laser frequency of the laser, or vice versa. The following examples provide techniques and devices for synchronizing a laser and an optical resonator with each other. In a specific example, the laser is operated and a laser output beam is generated at the laser frequency without modulating the laser beam. The laser light of the laser output beam is directed to the optical interferometer, the optical interferometer including a first optical path and a second optical path, which intersect to intersect the light in the first optical path and the second optical path. Optical interference is generated between the light in the optical path. The optical resonator is coupled to the first optical path and filters light in the first optical path. The two optical outputs of the optical interferometer are used to generate an error signal that represents the frequency difference between the laser frequency of the laser and the resonant frequency of the optical resonator. Then, using this error signal, either or both of the laser and the optical resonator are controlled and tuned to synchronize the laser and the optical resonator with each other.

  1A and 1B show two exemplary devices that synchronize the laser and the resonator with each other. The device of FIG. 1A synchronizes the resonator to the laser by tuning the resonator in response to the error signal, while the device of FIG. 1B resonates the laser by tuning the laser in response to the error signal. Synchronize with the vessel.

  1A and 1B, a laser output beam is generated using a laser 101 at a laser frequency, and the laser output beam is supplied to an optical interferometer 110. The optical interferometer 110 of this specific example is a Mach-Zehnder interferometer, and separates incident light into a first optical path including a reflector 114 and a second optical path including a reflector 116. An input beam splitter 113 is included. The first and second optical paths merge together at an optical combiner 115 and terminate. In this example, the optical coupler 115 is partially transmissive and partially reflective, transmits part of the light from the first optical path, and transmits light from the second optical path. May be an optical element that generates a first combined light output 111 (A) by reflecting a portion of the light. The optical coupler 115 transmits a part of the light from the second optical path, reflects a part of the light from the first optical path, and generates the second combined optical output 112 (B). Generate. The optical resonator 130 is optically connected to the second optical path, and filters light in the second optical path. A WGM resonator can be used as the resonator 130, and the WGM resonator can be coupled to the second optical path by evanescent coupling. The detection module 120 detects the first combined light output 111 and the second combined light output 112 to determine a frequency difference between the laser frequency of the laser 101 and the resonance frequency of the optical resonator 130. Generate an error signal that represents. Feedback control 140 is provided to receive the error signal and tune one of laser 101 and optical resonator 130 to synchronize laser 101 and optical resonator 130 with each other. In some implementations, both laser 101 and resonator 130 may be tuned to achieve synchronization.

  In FIG. 1A and FIG. 1B, the detection module 120 includes a photodetector, for example, a low speed photodiode, detects the white and dark ports of the interferometer 110, and the output of the photodetector is Subtraction is performed in the differential amplifier 121. The output of the amplifier 121 represents an error signal. If the two optical paths in the interferometer 110 are perfectly balanced, this output will be approximately zero voltage when the optical detuning between the laser 101 and the resonator 130 is zero. The phase of the light beam in the second optical path having the resonator 130 sharply depends on the resonance frequency of the resonator 130 and its bandwidth.

  The resonator 130 can be tuned based on various mechanisms. For example, a WGM resonator can be formed from an electro-optic material and can be tuned by changing an electrical control signal applied to the material. Further, the resonator can be tuned by controlling the temperature of the resonator or by applying a force or pressure that mechanically compresses the resonator using an actuator such as a PZT actuator.

  FIG. 2 shows signals A, B, and C in FIGS. 1A and 1B. FIG. 3 shows the output of the amplifier 121 operating under saturation conditions. The design of FIGS. 1A and 1B does not require optical modulation of the laser carrier from the laser and can be designed in a compact package. The feedback can be designed to provide sensitive and effective synchronization with high gain. Synchronization may be initiated automatically within the feedback equilibrium range.

  By using the differential signal of FIGS. 1A and 1B, the synchronization range is limited within the line width of resonance of the resonator 130. This operating range may be narrow and insufficient for certain applications.

  4A-4C and FIG. 5 show another example of a detection module 120 that provides broadband synchronization operation.

  FIG. 4A shows that one of the photodetector outputs is separated into two signals. 4B and 4C show signal and detection details for the design of FIG. 4A. One signal is phase shifted by 90 degrees by phase shifter 410 and the other signal is fed to differentiator 420 to produce a differentiated output of the same photodetector. Then, the two processed signals are supplied to the multiplier 430, and the multiplier 430 multiplies the two processed signals. The result is an error signal that results in zero output when the detuning between the laser frequency of laser 101 and the resonant frequency of resonator 130 is zero. The signal grows linearly from the zero detuning condition and has a wide bandwidth limited by the bandwidth of the RF component used in the detection module 120.

  FIG. 5 shifts the phase of the first combined light output 111 to perform a first signal processing unit 410 that generates a first signal and time differentiation of the second combined light output 112. Thus, a device that synchronizes the laser 101 and the resonator 130 with each other using the second signal processing unit 420 that generates the second signal is shown. The signal multiplier 430 is used to multiply the first signal and the second signal to generate a multiplied signal. The detection module 120 uses the multiplied signal to generate an error signal that indicates the frequency difference between the laser 101 and the resonator 130.

  FIG. 6 is a further illustrative example of synchronizing laser 101 and resonator 130 with each other using both the feedback technique shown in FIGS. 1A and 1B and the feedback technique shown in FIGS. 4A-4C and FIG. Devices are shown. In this example, device 410 is used to generate a first signal by shifting the phase of one of the two optical outputs of optical interferometer 110 by 90 degrees, and device 420 is the 2 of optical interferometer 110. Used to generate a second signal by performing a time derivative of the other of the two light outputs. The multiplier 430 multiplies the first signal and the second signal, calculates the multiplied signal, and generates a first error signal indicating the frequency difference. In parallel with this, using the differential amplifier 121, the power levels of the two optical outputs of the optical interferometer 110 as a second error signal representing the frequency difference between the laser frequency and the resonant frequency of the optical resonator. The difference signal is generated. Next, the feedback 140 uses both the first and second error signals as inputs to the other differential amplifier 610 and outputs as an error signal for synchronizing the laser 101 and the optical resonator 130 with each other. Is generated.

  The above technique was examined using an experimental setup based on a CaF2 high Q whispering gallery mode resonator filter. In this setup, a 1551 nm laser was used and the laser output was fed to a filter coupled to a fiber. The Mach-Zehnder interferometer was assembled with a fiber patch cord and a Newport direct fiber coupler. FIG. 7 shows the measured optical spectrum of the filter, and FIG. 8 shows a specific example of the error signal.

  Photonic filters based on whispering gallery mode resonators (wgmr) may require precise tuning of the frequency difference between the carrier frequency in various applications and the resonant frequency of wgmr is there. This difference determines the center of the filtering function of the photonic filter. For example, in some applications, the natural frequency of a single 15 MHz wide area CaF2wgm filter can be stabilized within a few MHz. This level of frequency stabilization may require thermal stabilization of the resonator within a temperature range of about 7 mK. This can be achieved using a PID driven thermoelectric cooler (TEC) and passive thermal isolation. In some applications, higher stability is required. For example, a 15 MHz balance filter uses the difference between the phases of two resonant lines. This requires stability at frequencies below MHz, which requires thermal stabilization at the 100 μK level. This level of thermal stabilization can be achieved using complex multi-stage TEC control techniques, but some of these techniques require careful thermal design of the filter and relatively bulky packaging.

  In the following, techniques and devices that control the frequency spacing between the laser carrier frequency of the laser and the mode of the resonator using the natural thermal nonlinearity of the resonator will be described. For example, FIG. 9 shows details of one device that stabilizes the resonance of the optical resonator. In this device, the laser 901 generates a laser output beam at the laser carrier frequency, and the optical resonator filter 920 is disposed in the optical path of the laser output beam and receives the light of the laser output beam. An optical coupler is provided for coupling the optical resonator 920 to the optical path, receiving the light of the laser output beam, and generating the optical output. The optical coupler provides optical coupling at an optical filter mode frequency different from the laser carrier frequency so as to provide optical coupling that is not under critical coupling conditions in which the light coupled to the optical resonator is completely trapped within the optical resonator. Constructed and arranged with respect to resonator 920. This device includes an optical modulator 910 between a laser 901 and an optical resonator 920 in the optical path of the laser output beam, and the optical modulator 910 modulates the laser output beam to generate a modulated sideband. However, the optical coupling of the light in the modulation sideband to the optical resonator 920 by the optical coupler is in the vicinity of the critical coupling condition, and the optical absorption of the light in the modulation sideband causes the resonator 920 to thermally Stabilize. The modulation sideband is different in frequency from the optical filter mode frequency. The TEC 930 is in thermal contact with the resonator 920 and controls the temperature of the resonator 920 through control by the TEC controller 940. This temperature control provides a coarse DC thermal bias that brings the resonator 920 near the desired thermal conditions. Then, using the modulated laser beam, precise thermal stabilization is performed in which the resonator 920 is thermally synchronized with the laser 101.

  The laser output beam is modulated at a frequency controlled by an RF source or synthesizer 912. The frequency position and intensity of the modulation service sideband can be precisely controlled by controlling the RF power and frequency of the synthesizer 912. The frequency of the modulation is selected so that the service sideband matches the auxiliary optical mode and this coupling is close to, but lower than, the critical coupling condition. The critical coupling condition for optical coupling between the optical coupler and the resonator is that the loss inside the resonator and the loss of optical coupling via the optical coupler are equal, and the light coupled to the resonator is completely in the resonator. A condition where the transmission of the captured and coupled light at the resonant frequency is zero. Under this design, the other modes of the resonator 920, i.e., the filtering mode used for the optical filtering operation, are strongly overcoupled, so that the filtered mode light is trapped in the resonator. Instead, it can pass through the resonator 920. Thus, the service mode and the auxiliary mode exhibit thermal nonlinearities that are significantly different from the filtering mode. As a result, in practice, only the auxiliary mode excited by the service sidebands affects the optical frequency of the resonator via thermal nonlinearity, and the signal filtered in the filtering mode is subject to the heating conditions of the resonator. Does not affect.

  Absorption of optical power in the auxiliary mode results in a reversible shift in the resonator temperature and a shift in the refractive index of the resonator. This change in temperature shifts the frequency of all optical modes near the cavity rim. Thermal non-linearity represents natural feedback that locks the optical power to the auxiliary mode. Cavity temperature variations or laser frequency variations cause optical heating or cooling of the cavity periphery that maintains the service sidebands in the gradient of the auxiliary light mode. The feedback gain of this thermal feedback depends on the thermal nonlinearity of the resonator, the mode volume, the thermal conductivity of the resonator body and the heat capacity.

  FIG. 10 shows the above-described frequencies for thermal stabilization based on the thermal effect of the service sideband in the resonator. Thus, the presence of light in the service sideband near the critical coupling condition synchronizes the filter mode frequency to the laser carrier frequency without a feedback control circuit. In some implementations, feedback control may be provided to further enhance thermal stabilization by the service sideband. For example, a photodetector can be used to monitor the transmission of light from the resonator in the service sideband, and feedback control can be used to control the laser frequency of the laser or the temperature of the resonator to Ensure that the waveband is at a resonance gradient near the critical coupling condition for the service sideband.

  This technique can excite the auxiliary optical power at completely different optical frequencies that do not affect the signal filtered at the filter mode frequency. The thermal nonlinearity of the filtering mode can be kept low. The laser frequency may drift over time, but even if the laser drifts due to thermal synchronization through the service sideband, it is between the laser carrier frequency and the wgmr resonant frequency. The frequency difference can be maintained. Therefore, a laser with high long-term stability is not required for this synchronization method.

  The proposed technique was tested using a 200 kHz CaF2 linear wgmr filter, an EOSPACE modulator and a Koheras 1550 nm laser. In order to measure the gain of the thermal feedback, the laser frequency was shifted by 100 MHz, and the relative shift was measured between the laser frequency and the mode resonance frequency as shown in FIG. With the service sideband having 120 μW optical power, the measured feedback time constant was about 500 ms and the gain was about 1000. At powers higher than 150 μW, this particular setup feedback became unstable.

  The measured frequency difference stability is about 100 kHz, which corresponds to about 1 degree phase stability in a balanced filter. Further improvements can be achieved by sub-modulated service sidebands that are sub-modulated at a frequency higher than the frequency of thermo-refractive oscillation. This type of sub-modulation suppresses thermorefractive oscillations and increases the power of the service sideband, resulting in increased feedback gain.

  In the operation of the optical resonator filter described above, which is stabilized by the service sideband, a resonator-controlled laser beam with a laser carrier frequency modulated to carry the modulation sideband is supplied to the optical resonator. An optical coupler is used to couple light in the modulation sideband to an optical resonator near the critical coupling condition and to thermally stabilize the resonator by light absorption of light in the modulation sideband. While the resonator receives and is stabilized by the resonator-controlled laser beam, the incident optical signal is directed through the optical resonator, and the modulated carrier and laser carrier of the resonator-controlled laser beam. Optical filtering of the incident optical signal is performed by resonance of the optical resonator at an optical filter mode frequency different from the frequency.

  Another optical synchronization is the synchronization of the laser to the resonator by injection locking. For example, by directing laser light from the laser to the WGM resonator and supplying the laser light from the WGM resonator to the laser via direct injection, the laser can be in whispering gallery mode for linewidth reduction and stabilization ( WGM) can be synchronized to the resonator. Part of the light passing through the resonator is reflected by the laser, and the laser frequency (wavelength) is synchronized with the high Q mode frequency of the resonator, narrowing its spectral line. When the WGM resonator is stabilized against environmental perturbations such as temperature fluctuations or vibrations, the modal frequency stability of the resonator is transferred to the laser frequency or wavelength. The WGM resonator can be formed from an electro-optic material and can be tuned by changing the electrical control signal applied to the material. For light injection locking, the laser wavelength or frequency can be tuned by applying a DC voltage applied to the resonator. Furthermore, the laser frequency can be phase and / or amplitude modulated by applying to the WGM resonator a microwave or RF field having a frequency that matches one or more free spectral regions of the resonator. The mode frequency of the resonator can be changed by applying temperature and pressure. In the case of a resonator formed of an electro-optic material, the mode frequency can be changed by the applied DC potential, so that the laser frequency (wavelength) can also be tuned. When the frequency of the laser is modulated by the application of a microwave signal to a DC current applied to the laser, the frequency (wavelength) of the laser remains synchronized to the resonator. As a result, a narrow linewidth laser that can be modulated can be obtained. When the WGM resonator is made of an electro-optic material, the intensity of the laser can be modulated by applying a microwave or RF electromagnetic wave to the resonator using an appropriate coupling circuit, and the laser is synchronized to the WGM resonator. Continue to be.

  FIG. 12 shows an exemplary device for synchronizing a laser to an optical resonator. The device includes a distributed feedback (DFB) laser that is tunable in response to a control signal and generates a laser beam at a laser frequency. The optical resonator supports a whispering gallery mode circulating in the optical resonator, is optically coupled to the DFB laser, receives a portion of the laser beam in the whispering gallery mode optical resonator, The whispering gallery mode laser light is returned to the DFB laser, the laser frequency is stabilized at the whispering gallery mode frequency, and the line width of the DFB laser is reduced. The device also includes a resonator tuning mechanism that controls and tunes the frequency of the whispering gallery mode and tunes the laser frequency of the DFB laser via feedback of the laser light from the optical resonator to the DFB laser. The optical coupler in this specific example is a prism coupler for both input coupling and output coupling. Coupling micro optics is disposed between the DFB laser and the resonator. The DFB laser has an inherently high Q value compared to other lasers, and thus provides better control over the selection of WG modes within the high density spectrum of the WGM resonator. Also, the WGM resonator can be tuned or controlled by applying stress by, for example, a PZT actuator that compresses the resonator, or by temperature control. As shown in the figure, the mount on which the laser device is formed is thermally controlled.

  This specification includes many details, but these details are not to be construed as limiting the scope of any invention or the claims, and are specific features of a particular embodiment. It is interpreted as a description. In this specification, several features disclosed in the context of separate embodiments may be combined and implemented in a single embodiment. Conversely, various features disclosed in the context of a single embodiment can be embodied separately in multiple embodiments and can be embodied in any suitable subcombination. Furthermore, although the above describes some features as functioning in a certain combination, initially, even if so claimed, from the claimed combination One or more features may be excluded from the combination in some cases, and the claimed combination may be changed to a partial combination or a variation of a partial combination.

  Only a few specific examples have been disclosed. From what has been described and illustrated in this application, it is clear that variations, extensions and other specific examples can be conceived.

Claims (25)

A laser that produces a laser output beam at a laser frequency;
A first optical path located in the optical path of the laser output beam for receiving a first portion of the laser output beam, a second optical path for receiving a second portion of the laser output beam, and the first and second (1) a part of light from the first optical path is transmitted, a part of the light from the second optical path is reflected, and the first And (2) transmitting a portion of the light from the second optical path and reflecting a portion of the light from the first optical path to produce a second combined light output. An optical interferometer having an optical coupler for generating optical output;
An optical resonator optically coupled to the first optical path and filtering light in the first optical path;
A detection module that detects the first combined light output and the second combined light output and generates an error signal representing a frequency difference between the laser frequency and a resonance frequency of the optical resonator. When,
Receiving the error signal and tuning one of the (1) the laser and (2) the optical resonator according to the frequency difference of the error signal to synchronize the laser and the optical resonator with each other; And a feedback control mechanism.   The device of claim 1, wherein the feedback control mechanism tunes the laser to synchronize the laser with a resonant frequency of the optical resonator.   The device of claim 1, wherein the feedback control mechanism tunes the optical resonator to synchronize a resonant frequency of the optical resonator with the laser.   The device of claim 1, wherein the detection module comprises a differential amplifier that generates a differential signal of power levels of the first combined light output and the second combined light output as an error signal. The detection module
A first signal processing unit for shifting the phase of the first combined light output to generate a first signal;
A second signal processing unit for performing a time differentiation of the second combined light output to generate a second signal;
A signal multiplier for multiplying the first signal and the second signal to generate a multiplied signal;
The device of claim 1, wherein the detection module generates an error signal indicative of the frequency difference using the multiplied signal.   6. The device of claim 5, wherein the detection module generates the error signal using a DC component of the multiplied signal. Receiving the first combined light output portion and the second combined light output portion; and receiving the first combined light output portion and the second combined light output portion. A second detection module comprising a differential amplifier that generates a differential signal of the power level of the portion as a second error signal representing a frequency difference between the laser frequency and the resonant frequency of the optical resonator;
The device of claim 5, wherein the feedback control mechanism synchronizes the laser and the optical resonator with each other using both the error signal and the second error signal.   The feedback control mechanism includes a second differential amplifier that receives the error signal and the second error signal and generates a differential output signal, wherein the feedback control mechanism responds to the differential output signal with the laser and the optical resonance. 8. The device of claim 7, wherein the devices are synchronized with each other.   The device of claim 1, wherein the optical resonator is a narrowband whispering gallery mode optical resonator. In a method of synchronizing a laser and an optical resonator with each other,
Generating a laser output beam at a laser frequency without operating the laser and modulating the laser beam;
An optical interferometer that includes a first optical path and a second optical path that intersect the laser light of the laser output beam, and generates optical interference between the light in the first optical path and the light in the second optical path. Step to orient to,
Optically coupling an optical resonator in the first optical path to filter light in the first optical path;
Using the two optical outputs of the optical interferometer to generate an error signal representing a frequency difference between the laser frequency of the laser and the resonant frequency of the optical resonator;
And (1) tuning one of the laser and (2) the optical resonator in response to the frequency difference of the error signal to synchronize the laser and the optical resonator with each other.   The method according to claim 10, further comprising: generating a difference signal between power levels of the two optical outputs of the optical interferometer as the error signal. Shifting one phase of the two optical outputs of the optical interferometer by 90 degrees to generate a first signal;
Performing a time derivative of the other of the two optical outputs of the optical interferometer to generate a second signal;
11. The method of claim 10, further comprising: multiplying the first signal and the second signal to calculate a multiplied signal and generating the error signal indicative of the frequency difference.   The method of claim 12, wherein an error signal is generated using a DC component of the multiplied signal. Generating a difference signal between the power levels of the two optical outputs of the optical interferometer as a second error signal representing a frequency difference between a laser frequency and a resonance frequency of the optical resonator;
13. The method of claim 12, comprising synchronizing the laser and the optical resonator with each other using both the error signal and the second error signal. In a device that stabilizes the resonant frequency of the optical resonator with respect to the laser frequency from the laser,
A laser that generates a laser output beam at a laser carrier frequency;
An optical resonator disposed in an optical path of the laser output beam and receiving the light of the laser output beam;
The optical resonator is coupled to an optical path, receives light of the laser output beam, generates optical output, and the light coupled to the optical resonator is at the optical filter mode frequency different from the laser carrier frequency. An optical coupler configured and arranged with respect to the optical resonator to provide optical coupling that is not under critical coupling conditions that are completely trapped within the resonator;
An optical modulator disposed in the optical path of the laser output beam between the laser and the optical resonator and modulating the laser output beam to generate a modulated sideband; Optical coupling of the light in the modulation sideband to the optical resonator is near the critical coupling condition, and the optical resonator is thermally stabilized by light absorption of the light in the modulation sideband. The modulation sideband has a frequency different from that of the optical filter mode frequency.   The device of claim 15, comprising a temperature controller that controls the temperature of the optical resonator so that the optical resonator is near a critical coupling condition in a modulation sideband.   The device of claim 15, wherein the optical resonator is a whispering gallery mode resonator.   A mechanism for directing an optical signal having a spectral component near the optical filter mode frequency, passing the optical resonator, and optically filtering the optical signal by resonance of the optical resonator at the optical filter mode frequency The device of claim 15. In a method of operating an optical resonator filter,
Providing an optical resonator with a resonator-controlled laser beam having a laser carrier frequency modulated to carry a modulation sideband;
Operate an optical coupler to couple light in the modulation sideband to the optical resonator near a critical coupling condition where the light coupled to the optical resonator is completely trapped in the optical resonator. Thermally stabilizing the optical resonator by light absorption of light in the modulation sideband;
While the optical resonator receives the optical resonator control laser beam and is stabilized thereby, directs an incident optical signal through the optical resonator to control the modulation sideband and the resonator control Performing optical filtering of an incident optical signal by resonance of the optical resonator at an optical filter mode frequency different from the laser carrier frequency of a laser beam.   A temperature controller coupled to the optical resonator is used to control the temperature of the optical resonator so that the optical resonator is near the critical coupling condition in the modulation sideband. Item 20. The method according to Item 19.   The method of claim 19, wherein the optical resonator is a whispering gallery mode resonator. In a device for synchronizing a laser to an optical resonator,
A distributed feedback (DFB) laser that is tunable in response to a control signal and generates a laser beam at a laser frequency;
Configured to support a whispering gallery mode circulating in the optical resonator, optically coupled to the DFB laser, and receiving a portion of the laser beam in the optical resonator in the whispering gallery mode Optical resonance that returns the whispering gallery mode laser light in the optical resonator back to the DFB laser, stabilizes the laser frequency at the whispering gallery mode frequency, and reduces the line width of the DFB laser. And
A resonator tuning mechanism that controls and tunes the frequency of the whispering gallery mode and tunes the laser frequency of the DFB laser via feedback of the laser light from the optical resonator to the DFB laser . The optical resonator includes an electro-optic material that changes a refractive index according to an electric signal applied to the optical resonator,
23. The device of claim 22, wherein the resonator tuning mechanism applies and controls the electrical signal to tune the laser frequency of the DFB laser.   23. The device of claim 22, wherein the resonator tuning mechanism controls and tunes the temperature of the optical resonator to tune the laser frequency of the DFB laser.   23. The device of claim 22, wherein the resonator tuning mechanism tunes the laser frequency of the DFB laser by applying and controlling pressure applied to the optical resonator.

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